Enhanced Wettability Alteration by Surfactants with Multiple Hydrophilic Moieties

Abstract

The main production mechanism during water flooding of naturally fractured oil reservoirs is the spontaneous imbibition of water into matrix blocks and resultant displacement of oil into the fracture system. This is an efficient recovery process when the matrix is strongly waterwet. However, in mixed-to oil-wet reservoirs, secondary recovery from water flooding is often poor. Oil production can be improved by dissolving low concentrations of surfactants in the injected water. The surfactant alters the wettability of the reservoir rock, enhancing the spontaneous imbibition process. Our previous study revealed that the two main mechanisms responsible for the wettability alteration are ion-pair formation and adsorption of surfactant molecules through interactions with the adsorbed crude oil components on the rock surface. Based on the superior performance of surfactin, an anionic biosurfactant with two charged groups on the hydrophilic head, it was hypothesized that the wettability alteration process might be further improved through the use of dimeric or gemini surfactants, which have two hydrophilic head groups and two hydrophobic tails. We believe that when ion-pair formation is the dominant wettability alteration mechanism, wettability alteration in oil-wet cores can be improved by increasing the charge density on the head group(s) of the surfactant molecule since the ion-pair formation is driven by electrostatic interactions. At a concentration of 1.0 mmol L -1 a representative anionic gemini surfactant showed oil recoveries of up to 49% original oil-in-place (OOIP) from oil-wet sandstone cores, compared to 6 and 27% for sodium laureth sulfate and surfactin, respectively. These observations are consistent with our hypothesis.

Adsorption Properties of Gemini and Monomeric Cationic Surfactants on Sandstone and Silica Nanoparticles

“…It can be concluded from Figure 3 that the adsorption amount of CTAB, GC 16 and GC 12 Table 1. The equilibrium adsorption amount of GC 16 with double chains and double heads on NPS is 22.01 μmol/g, while that of CTAB is 14.96 μmol/g.…”

“…The highest concentration of GC 16 CTAB and GC 12 , and above that of GC 16 . The adsorption of surfactants in different adsorption time was determined to obtain plots of the adsorption amount of the solution of CTAB, GC 16 and GC 12 on solid sandstone and NPS surface versus soaked time at 45˚C, as is shown in Figure 4.…”

“…The CMC values of GC 16 , GC 12 and CTAB at 25˚C are 0.03 mmol/L, 1.0 mmol/L and 0.8 mmol/L, respectively. Figure 1 shows the chemical structure of these Gemini surfactants.…”

“…For crushed sandstone, the adsorption amounts of GC 16 and CTAB are 4.91 μmol/g and 7.87 μmol/g, respectively, which shows that the adsorption amount of Gemini surfactant GC 16 on solid surface is greater than that of the single-chain surfactant CTAB. In addition, it is seen that the maximum adsorption of GC 16 on the solid surface including sandstone and NPS is slightly larger than that of GC 12 , which indicates that the length of hydrophobic alkyl affects the equilibrium adsorption amount, in a word, the adsorption increases with the increase of alkyl carbon number of cationic surfactant molecules with the similarity structure. …”

“…Surfactant injection as a method of a chemical flooding can enhance oil recovery by reducing the interfacial tension (IFT) between oil and water, forming O/Wemulsions, altering the rock wettability and thus resulting from the adsorption of surfactants on reservoir rock [1] [2] [3]. The adsorption of different surfactants, including anionic surfactant, nonionic surfactant, and zwitterionic surfactant on various solid/water interfaces, has been extensively studied by many authors [4]- [12].…”